MONACA, Pa. - An explosion Thursday at a zinc smelting plant in western Pennsylvania killed two people and injured at least one, authorities said.

A worker who initially had been reported missing was among the dead, Beaver County emergency dispatcher Kevin Joy said. The rest of the work force at the Horsehead Corp. facility was accounted for after the blast.

The explosion, which occurred around 4:30 p.m., involved a refinery column that produces zinc oxide, Horsehead spokesman Ali Alavi said. The facility has about 600 employees, he said.

One worker complained of neck pain and was being checked out at a hospital, Alavi said. No other injuries were immediately reported.

County Coroner Teri Tatalovich-Rossi said the names and causes of death of the two victims would not be released until Friday, pending the results of autopsies and notification of families.

An investigation is under way to determine the cause of the explosion, Alavi said. Despite initial reports that a fire had broken out, he said: "My understanding was that there was no fire. There was an explosion, but no resulting fire."

Wesley Hill, director of Beaver County Emergency Services, said Friday night that the explosion caused no risk to the public. The plant lies at a country crossroads about a mile south of a large shopping mall.

Outside the plant, which was surrounded by fencing, workers could be seen going in and out of the building but none would talk to reporters who had gathered at the entrance.

A half-mile down the road, workers at the World Famous Midway Bar & Grill, a regular hangout for plant workers, said emergency crews had used the bar's gravel parking lot as a staging area shortly after the blast.

The mood there was heavy, bartender Mary Jordon said.

"I mean they're like family, they all come here," she said. "It's very sad. Our prayers are with them and with the families."

Terri Marcellus, 41, of nearby Chippewa, said her boyfriend was part of a roving maintenance crew at the plant when the explosion happened, but he was not affected.

"He called me twice. The first time he called me I could tell he was upset and he said that they had two missing," she said. "The last time I talked to him ... he said, `We got two gone.'"

According to its website, the U.S. Occupational Safety and Health Administration issued citations with proposed penalties of $186,750 in January 2006 at the facility. The results came after an investigation into why an employee stepped into an "uncovered condenser pit full of molten zinc" and suffered severe burns to his legs, according to the site.

OSHA also issued 27 "serious citations" for alleged violations that included a failure to use an approved safety platform, provide guardrails and protection barriers. The agency issued 14 "other-than-serious" violations for "failing to maintain required records of employee exposures to lead and cadmium."

On its website, Horsehead said the electrothermic zinc smelter in Monaca, which is about 30 miles north of Pittsburgh, "operates as the country's largest."